Ink jet printers, and in particular, drop-on-demand ink jet printers having print heads with acoustic drivers for ink drop formation, are well known in the art. The principle behind an impulse ink jet of this type is the generation of a pressure wave in an ink chamber and subsequent emission of ink droplets from the ink chamber to a nozzle orifice as a result of the pressure wave. A wide variety of acoustic drivers have been employed in ink jet print heads of this type. For example, such drivers may consist of a transducer formed by piezoceramic material bonded to a thin diaphragm. In response to an applied voltage, the diaphragm displaces ink in the ink chamber and causes a pressure wave and the consequent flow of ink to one or more nozzles. other types of acoustic drivers for generating pressure waves in ink include heater-bubble source drivers (so called bubble jets) and electromagnet solenoid drivers.
Known ink jets typically combine an ink jet print head, from which drops of ink are ejected toward a record medium, with a reservoir for supplying ink, including plural colors of ink, to various nozzles of the ink jet print head. Also, it is common to shuttle or scan an ink jet print head transversely across a record medium as the medium is being printed by the print head.
In a typical application, record media (a sheet of paper, for example) is delivered to a drum and secured to the drum for subsequent printing by a mechanism, such as a clamp, that grips one edge of the medium. As the drum rotates past a printing location, ink is ejected from the print head onto the medium to accomplish the printing. In a typical printing arrangement, the medium is, in effect, printed in rows of pixels, each pixel (picture element) having a predetermined size and height. The height of the pixel corresponds to a distance along the medium in the direction of rotation of the drum.
One exemplary printer is shown in U.S. Pat. No. 4,581,618 Watanabe et al. In Watanabe, record medium is fed by a roller mechanism to a first pinch roller which bears against a drum. This drum is described as being a platen of high friction material, such as rubber. Soft rubber rollers would not have a precise radius, particularly at locations where engaged by other rollers. A motor 10, described as a "feed pulse" motor, is used to drive the drum and the paper transport mechanism of the printer. An elaborate multiple gear drive system is used to couple the motor to the drum and other paper transport rollers of the system. At the appropriate time, the medium is transferred from the first roller to the drum, with the medium being retained on the drum by a movable pinch roller illustrated in this patent as having a gap in its center. The movable pinch roller retains the paper on the drum by torque established by a friction clutch. During printing, the drive mechanism is described as rotating the drum through a predetermined angle after the printing of each line of print.
Because gears are used in the paper transport mechanism of this device, backlash can occur which can result in inaccurate positioning of the paper during the printing operation. Also since gears typically have very few teeth which engage one another at any given time, variations in the configuration of particular teeth of a gear translate to inaccuracies in the transportation of the record medium through the printer. In addition, a drive mechanism that relies on a multiplicity of gears is subject to wear and mechanical failure.
U.S. Pat. No. 4,707,704 to Allen et al. mentions the use of a stepper motor for driving a drum of an ink jet printer. In this patent, the stepper motor is shown coupled directly to the shaft of the drum. With this construction, the inertia of the drum is applied directly to the motor shaft and can cause a very poor inertia match between the motor and the load on the motor. In addition, this patent discloses a transport path in which a roll of record media is positioned within a drum and moved by an internal roller, including one covered with resilient material, to the exterior of the drum for printing.
Prior art printers have also employed numerous types of clamps for securing record media to a drum during printing operations. U.S. Pat. No. 4,815,870 to Sparer et al. discloses a sheet clamp for a thermal printer drum in which the clamp is positioned within a recess of the drum. The drum is rotated in one direction during printing and in a reverse direction during sheet ejection.
Still another clamping device is shown in U.S. Pat. No. 4,386,771 Lakdawala for a facsimile machine. In this device, a gripping bar grips the edge of a sheet to hold it onto a drum. The direction of rotation of the drum is reversed to eject the sheet from the drum with a guide and a sheet scraper being utilized to remove the sheet from the device.
The use of pressure fixing rollers for fusing or spreading phase-change or hot-melt ink on record media is also known. Japanese Patent No. 18,351 to Moriguchi et al., U.S. Pat. No. 4,745,420 to Gerstenmeier and U.S. Pat. No. 4,889,761 to Titterington et al. are examples. Other examples of prior art image fixing apparatus including rollers are described in U.S. Pat. Nos. 3,293,059 to Stole, 3,566,076 to Fantuzzo and 4,568,949 to Muranaka. These existing fusing rollers typically apply an extremely high loading force along the line of contact between fusing rollers, e.g., 100 lbs. per lineal inch. In this case, for a ten inch long roller, 1,000 lbs. of force must be applied. Consequently, the structural support for such fusing rollers is typically relatively heavy and bulky in order to withstand extremely high forces.
Although a number of printers and printer drive mechanisms are known, a need exists for an improved ink jet printer which is capable of overcoming these and other disadvantages of the prior art.